Doramectin efficacy against gastrointestinal nematodes in pigs

Four controlled trials with growing pigs were performed to determine efficacy of doramectin against natural and induced populations of nematodes. In Trial 1 (T1), 20 pigs with natural infections were assigned to one of two like groups on the basis of weight, sex and worm egg counts. In Trial 2 (T2), 20 pigs with negative worm egg counts were assigned to one of two groups on the basis of weight and sex. Each pig was subsequently given (per os) 3000 Trichuris suis embryonated eggs; 2000 Ascaris suum embryonated eggs; 10 000 Oesophagostomum spp. infective larvae and 10 000 Strongyloides ransomi infective larvae (SC injection). In Trial 3 (T3), 20 pigs with negative worm egg counts were assigned as in T2, and each pig was subsequently given (per os) 2000 A. suum embryonated eggs, 15 000 Oesophagostomum quadrispinulatum infective larvae, and 2891 Hyostrongylus rubidus infective larvae. In Trial 4 (T4), 16 pigs with negative worm egg counts were each assigned to one of two groups as in T2 and were given (per os) 2670 T. suis embryonated eggs. On Day 0 of each trial, each pig of the control group was injected IM in the neck with sterile saline at the rate of 1.5 ml 50 kg −1. Each pig in the treated group of each trial was similarly injected with doramectin at the rate of 300 μg kg −1. All pigs were necropsied 14 or 15 days post-treatment and parasites recovered by standard parasitological procedures. Efficacies against natural infections were: A. suum, 100%; Oesophagostomum spp. 100%; H. rubidus, 99.4%; and Strongyloides ransomi, 99.9%. Efficacies against induced infections were: 4th stage A. suum, 100%; 4th stage O. dentatum, 99.9%; 4th stage O. quadrispinulatum, 97.1 and 99.6%; 4th stage H. rubidus, 100%; adult S. ransomi, 100%; adult Trichuris suis in mixed infection, 54.1%; and in pure infection, 95.3%.